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()UANTITATIYK   ESTIMATION

27

into the outer jacket and the vapours are condensed by an
upright condenser or tube which is attached to the outlet tube.
The crucible is placed within and
covered with a metal lid. There is a
small aperture to admit air from below
into the inner vessel and a corresponding
outlet in the lid. Aniline, b.p. 182°,
may be used in the outer jacket in the
present case. The (iooch crucible is
weighed and fitted to a filter flask and
the silver halide filtered and washed at
the pump. The crucible is -then heated
in the air-bath until the weight is con-
stant (^ hour) and weighed. The re-
sult is calculated in percentage of
halogen.

Extwiplc......Bromacetanilide gave  the

following result :-.......

o'l 5 i gram gave 0*134 gram AgHr.

l-'lli.   116.

• ==77-51 per
188x0-151        J        *

Calculated for CsIl,BrNO ; Hr = 37-38
per cent.

Another Method (Piria and Schrff).—There are some
substances which are incompletely decomposed with fuming
nitric acid under the conditions described above, and the results
are consequently too low. In such cases the following method
may be employed. The substance is weighed into a very small
platinum crucible, which is then filled up with a mixture of
anhydrous sodium carbonate (i pail) and pure powdered quick-
lime (4 to 5 parts). The crucible is then inverted in a larger
crucible, the space between the two being filled with the same
mixture of sodium carbonate and lime. The large crucible is
now heated, first with a small blow-pipe flame, and then
more strongly until the mass is red hot. The contents are then
allowed to cool, and dissolved in a large excess of dilute nitric
acid. The substance must be added slowly and the acid kept
cool. The halogen is then precipitated with silver nitrate and
estimated in the usual way.

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